A dielectric porcelain composition tends to exhibit an increased dielectric loss as the frequency used becomes high. Therefore, a dielectric porcelain composition which exhibits a high relative dielectric constant (hereinafter referred to as ".di-elect cons..sub.r ") and a high unloaded Q value (i.e., high coefficient of unloaded quality) (hereinafter referred to as "Qu") in the microwave frequency range has been desired. As this kind of a dielectric porcelain composition there has heretofore been known one having a crystalline structure comprising two phases, i.e., perovskite phase and illmenite phase (as disclosed in JP-A-2-129065 (The term "JP-A" as used herein means an "unexamined published Japanese patent application")). A dielectric porcelain composition comprising MgTiO.sub.3 and TiO.sub.2 mixed with a predetermined amount of CaTiO.sub.3 has been known as well (as disclosed in JP-A-52-118599).
However, the former dielectric porcelain composition is disadvantageous in that it contains a considerable amount of other components such as Nd.sub.2 O.sub.3, La.sub.2 O.sub.3, PbO and ZnO and doesn't always have a high Q.sub.u. The latter dielectric porcelain composition comprises TiO.sub.2 as an essential component and thus is disadvantageous in that the temperature coefficient of resonant frequency (hereinafter referred to as ".di-elect cons..sub.f ") makes a great positive or negative change when the mixing ratio of CaTiO.sub.3 falls within a range of from 3 to 10% by weight, making it difficult to adjust the temperature coefficient .di-elect cons..sub.f to a small value close to zero.